This invention relates generally to gas turbine engines and more particularly to a clamp for securing tubes within the engine against movement, including vibratory movement.
A gas turbine engine such as that used for powering an aircraft in flight includes numerous tubes for channeling various fluids through the engine during operation. Conventional clamps are used for mounting tubes to various points on the engine casing to accurately position the tubes and prevent their movement during operation of the engine. Since the gas turbine engine includes various rotating components, the tubes are subject to vibratory excitation that must be controlled for preventing vibratory fatigue damage thereto. Therefore, it is common to use clamping assemblies for mounting tubes to other tubes to further control vibrations in the tubes.
One exemplary conventional tube-to-tube clamping assembly used in a gas turbine engine includes a bracket abutting each of two tubes to be clamped together. Each tube is clamped to the bracket by a corresponding strap clamp. The strap clamps are semi-circular pieces that fit over the tubes and are bolted to the bracket. In order for the strap clamps to securely clamp their respective tube to the bracket, the tube diameter is slightly greater than the depth of the semi-circular portion of the strap clamps. Thus, a gap exists between each strap clamp and the bracket prior to the bolts being torqued. Torquing the bolts closes the gap and clamps the tubes to the bracket, and thus to one another. However, the clamping assembly is not positively located with respect to the tubes since the bracket is not attached to the engine casing or another bracket. The clamping assembly thus must be visibly located by markings etched on the tubes. Consequently, the clamping assembly location can vary significantly on the tubes which causes a large gap variation.
An excessively large clamp gap cannot be fully closed with the bolt torque load at installation because of the general inflexibility of the conventional semi-circular strap clamp. An unclosed gap can cause relaxation of the bolt joint preload and subsequent joint failure. This condition can occur not only in tube-to-tube clamping assemblies but also in any clamp design that is not positively located or has significant stiffness due to large strap thickness.
Accordingly, there is a need for a clamping assembly that has increased strap clamp flexibility to accommodate a large variation in clamp gaps.